40G MONOGRAmS OF NORTH AMERICAN RODENTIA. 



extension seen in the latter. The posterior palatine foramina form a large 

 circular opening, which is not extended forward beyond the intermaxillo- 

 niaxillary suture. The palate, owing to the more depressed form of the skull, 

 is much nearer the vomer than in Lcpus. The angular process of the lower 

 jaw is narrower, longer, and more recurved than in the Hares. The condylar 

 process is broad and quadrate, and the condyles have a very great antero- 

 posterior development, relatively four times greater than in Lcpus ; the 

 coronoid process is placed lower, and forms a mere tubercle, with a second 

 smaller tubercle near the last molar. The foramen mentum is remarkable 

 for its posterior position, being about opposite the middle true molar, instead 

 of considerably in advance of the first premolar, as is usually the case. 

 The small posterior upper molar seen in Lepus is wanting ; the remaining 

 upper molars do not differ materially from those of Lcpus, except that they 

 are much more deeply grooved on the inner side. The lower molars, how- 

 ever, are very different from those of Lcpus, they being so deeply divided by 

 the lateral grooves that the triturating surface presents a series of acute 

 triangles with open intervals, somewhat as in Arvicola. The cutting-edge of 

 the front upper incisor is gouge-shaped instead of chisel-shaped, as in Lcpus 

 and most other Rodents, the cutting-edge being hollowed on the inner side. 

 The anterior face is divided by a deep longitudinal groove into two unequal 

 moieties, the outer of which is nearly three times as wide as the inner, and 

 considerably longer, generally exceeding the inner, in Lagonajs princcps, by 

 about 0.05 of an inch. The cutting-edge is consequently deeply notched ; the 

 bottom of the notch, formed by the groove, being sometimes 0.12 of an inch 

 below the outer eds^e. The lower incisors are rounded anteriorlv, and lack 



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the groove seen in the upper incisors. 



The Pikas are nearly tailless, and the general form of the body and limbs 

 is much as in the Arvicola. They hence lack the greatly disproportionate 

 development of the hind limbs seen in the Hares. The clavicles are also well 

 developed. The toes are five in front and four behind, armed with short, 

 arched, compressed nails, and at the base of each toe is a prominent, naked 

 pad. The pelage is much firmer than in the Hares, with less of the soft, 

 downy under-fur, and more resembles the pelage of Arvicola. They are weak, 

 sedentary animals, living among loose rocks in alpine localities, generally on 

 or near the summits of high mountains, and are apparently strictly diurnal in 

 their habits. They are social in their dispositions, living generally in com- 



